Layer mutes / mute groups would be very nice. Some DAW platforms allow tracks to be grouped in folders. This could be a way to ease display congestion. ie, in one display mode, you might see the folders (drums, bass, leads, samples) etc. if you select a group or folder, you can access the contents, so by selecting (drums), you essentially 'zoom in' to see Kick, Snare, Hats, This dosen't mean adding tracks, but instead adds a mute layer which would allow sections of the key range (or even individual keys) to be muted, hence you could mute the kick part, or mute a sub-octave bass part, or lead harmony part. Perhaps the mute could also allow a quick and dirty transpose, so for that layer you could mute, or play the kick part temporarily as a tom, or combined kick/cymbal. Or the bass suboctave could become a diatonic harmony part...